With advances in network technologies, users are able to interact in many different ways with services and content provided via networks. For example, a user of a computing device is able to purchase goods from online retailers, post comments on online content such as news articles or blogs, participate in message boards, and participate in user surveys and polls. Through such interactive network-based services and content, users may interact not only with computers and software applications that provide network services and content, but also with other users, thus providing a rich experience for the users.
Unfortunately, automated software applications have been developed to mimic human interactions with computer interfaces through which network-based services and content are accessed, often for malicious purposes. For example, malicious bots may add large amounts of spam, such as advertising links, on comment boards and other online content, repeatedly vote in polls to skew poll results, carry out denial of service attacks, harvest email addresses for spamming, and artificially increase traffic numbers for certain websites or online content. While some security measures have been developed to detect non-human interaction with computer interfaces and deny access to network-based services and content by non-human users, malicious bots are increasingly able to bypass conventional security measures.